An ultrasonic study of point defects in electron-irradiated P-type silicon
Johnson, Ward Lewis
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https://hdl.handle.net/2142/25224
Description
Title
An ultrasonic study of point defects in electron-irradiated P-type silicon
Author(s)
Johnson, Ward Lewis
Issue Date
1987
Doctoral Committee Chair(s)
Granato, A.V.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
ultrasonic waves
point defects in crystals
electron-irradiated P-type silicon
Language
en
Abstract
The mechanisms of interaction of ultrasonic waves with point defects in
crystals are reviewed and a perturbation approach is introduced which leads to
general expressions for the resonance and relaxation strengths in terms of
matrix elements of the ultrasonic perturbation. These expressions provide the
basis for a discussion of the polarization dependence of resonance and
relaxation. Selection rules for cubic crystals are presented.
An exploratory ultrasonic study is performed on electron-irradiated Bdoped
and Al-doped silicon. Neutral substitutional boron is detected before
irradiation, as expected from previous ultrasonic studies on unirradiated
silicon. This defect produces both resonance and relaxation. Similar effects
are observed for substitutional aluminum. After irradiation, a relaxation is
observed when the sample is exposed to 0.18-0.39 eV light. By comparison with
previous EPR results, this relaxation is identified as the singly positively
charged state of the vacancy, v+. Preliminary results on the relaxation time
and strength of v+ suggest that it may have several populated vibronic levels.
Another relaxation is observed in irradiated Al-doped silicon when the sample
is exposed to white light. From its annealing behavior and dopant dependence,
we identify it as a non-equilibrium charge state of interstitial aluminum. The
most likely states appear to be Ali 0 and Ali-. Analysis of the polarization
dependence of the relaxation leads to the conclusion that the aluminum atom
rests at a Td interstitial site and the surrounding lattice is Jahn-Teller
distorted with e-type (tetragonal or <100> orthorhombic) symmetry.
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